1. Field of the Invention
The present disclosure relates to a method for manufacturing oxide fuel pellets and oxide fuel pellets manufactured thereby.
2. Description of the Related Art
Nuclear power generation uses heat generated by the nuclear fission. Oxide fuel pellets are put into a zirconium alloy cladding tube to seal each of both ends of the zirconium alloy cladding tube by welding, thereby manufacturing a fuel rod. Then, several fuel rods to several hundred fuel rods are bundled with each other to manufacture one assembly or bundle. The assembly or bundle may be fed into a light-water type power reactor or heavy-water type power reactor. Here, heat generated from the oxide fuel pellets is transferred into cooling water that flows around the fuel rods through the cladding tube via the oxide fuel pellets.
A nuclear fuel may be prepared as cylindrical or globular oxide fuel pellets that are manufactured by compacting and sintering a single or mixed material of oxides such as uranium (U), plutonium (Pu), or thorium (Th). The oxide fuel pellets are generally formed of uranium dioxide (UO2). Alternatively, the oxide fuel pellets may be formed of a material that is prepared by adding at least one of other nuclear fuel materials such as oxides of Pu, Th, Gd, and Er to uranium dioxide (UO2). Particularly, the oxide fuel pellets may be formed of (U,Pu)O2, (U,Th)O2, (U,Gd)O2, (U,Er)O2, (U,Pu,Gd)O2, or (U,Th,Pu)O2.
Uranium dioxide (UO2) pellets may be widely known as the nuclear fuel pellets. A method for manufacturing the uranium dioxide (UO2) pellets includes a process of adding and mixing a lubricant into/with uranium oxide powder that is used as a starting material to perform a preliminary compaction process at a pressure of about 1 ton/cm2, thereby manufacturing slug, a process of pulverizing the slug to produce granules, a process of adding and mixing a lubricant into/with the produced granules to perform a compression-compaction process, thereby manufacturing green pellets having a theoretical density (T.D) of about 50%, and a process of sintering the green pellets at a temperature of about 1,600° C. to about 1,800° C. for about 2 hours to about 4 hours under a hydrogen-containing gas atmosphere. The manufactured uranium dioxide pellets may have a density of about 95% of a theoretical density and a grain size of about 5 μm to about 25 μm.
However, when the green pellets are sintered at a high temperature of about 1,600° C. or more under the hydrogen atmosphere as described above, the risk of explosion of hydrogen may be involved. Also, electricity may be excessively consumed due to the sintering at the high temperature, and thus, the above-described manufacturing process may be uneconomical.
Also, in the low-temperature sintering method according to the related art, a method in which a sintering process is performed at a low temperature (about 1,400° C. or less) under an atmosphere in which a ratio of carbon dioxide/carbon monoxide is adjusted. However, in the low-temperature sintering method, it may be difficult to adjust the ratio of carbon dioxide/carbon monoxide, and thus it may be difficult to manufacture oxide fuel pellets that are adequate for nuclear fuel specification.
Thus, while the inventors study methods for manufacturing oxide fuel pellets, the inventors have developed a method in which green pellets are manufactured by using nuclear fuel powder containing uranium dioxide (UO2), and the manufactured green pellets are sintered and reduced by using an atmosphere gas at a low-temperature of about 1,400° C. to manufacture oxide fuel pellets that are adequate for nuclear fuel specification.